1. Field of the Invention
In addition to unit injectors and unit pumps, modern autoignition internal combustion engines use accumulator injection systems for injecting fuel. These accumulator injection systems include a high-pressure accumulator that is supplied with highly pressurized fuel by a high-pressure pump. The high-pressure pump represents the interface between the high-pressure part and the low-pressure part of injection system. The high-pressure pump can be associated with a pressure control valve, which on the one hand, opens when the pressure in the high-pressure accumulator is too high, thus allowing fuel to flow out of this accumulator via a manifold and back to the fuel tank and on the other hand, when the pressure in the high-pressure accumulator is too low, seals the high-pressure side off from the low-pressure side.
2. Prior Art
The publication “Diesel Motor Management”, 2nd updated and expanded edition, Vieweg 1989, Braunschweig; Wiesbaden, ISBN 3-528-03873-X, page 270, FIG. 9 has disclosed a pressure control valve used in a high-pressure pump, see page 267, FIG. 7. The pressure control valve includes a ball valve, which has a ball-shaped closing body. The pressure control valve contains an armature that is acted on by a compression spring at one end and is acted on by an electromagnet at the opposite end. For lubrication and cooling, fuel circulates around the armature of the pressure control valve.
If the pressure control valve is not actuated, then the high pressure prevailing in the high-pressure accumulator or at the outlet of the high-pressure pump also travels to the pressure control valve via the high-pressure supply line. Since the electromagnet exerts no force when it is without current, the high-pressure force overcomes the force of the compression spring, causing the pressure control valve to open; the pressure control valve remains open for more or less time depending on the fuel quantity delivered.
By contrast, if the pressure control valve is actuated, i.e. the electromagnet is supplied with current, then the pressure in the high-pressure circuit increases. To that end, a magnetic force is generated in addition to the force exerted by the compression spring. The pressure control valve is closed until a force equilibrium is established between the high-pressure force on the one hand and the spring force and magnetic force on the other. The magnetic force of the electromagnet is proportional to the activation current I of the magnet coils inside the pressure control valve. The activation current I can be pulsed using pulse-to-width modulation.
According to the above-mentioned publication, page 270, FIG. 7, the pressure control valve is flange-mounted, for example laterally, to the high-pressure pump. It is also possible for the pressure control valve and the high-pressure accumulator (common rail) to be sealed on the high-pressure side. In this case, the high-pressure accumulator (common rail) and the pressure control valve are each embodied as a separate respective component. These separately embodied components of the accumulator injection system, however, are costly to produce because their high-pressure side sealing locations require precision machining. In addition, the high-pressure side sealing locations must be provided with sealing elements capable of withstanding the mechanical stresses that occur at the high-pressure side sealing locations. With operation over time, the pressure level prevailing on the high-pressure side inevitably causes leaks to occur at the sealing locations disposed on the high-pressure side.
In addition, space problems can arise because lines are required between the high-pressure accumulator and the pressure control valve due to the size and installation orientation of these accumulator injection system components within the space. If separate components are joined, then their installation inside the engine compartment, in the cylinder head region of an autoignition internal combustion engine is difficult and the installation is time-consuming. In addition, temperature problems with regard to the control seat can arise when the components, i.e. the high-pressure accumulator and pressure control valve, are sealed off from each other on the high-pressure side. The control seat is the point at which a closing element embodied as a ball-shaped closing body is pushed into a seat by an armature part of the pressure control valve. The precise position of this seat, in turn, determines the air gap that is set between the armature plate and an end surface of the magnet core in a pressure control valve that is controlled by a solenoid valve. The more precisely the air gap between these components of the pressure control valve can be embodied, the more precisely a pressure difference Δp can be produced in accordance with a tolerance that is set in the pressure control valve. If the seat surface into which the ball-shaped closing element is pressed is deformed by an impermissibly intense heating due to an uneven temperature distribution, then after extended operation and the attendant temperature increase in the high-pressure accumulator, a change in the air gap occurs due to the changing air gap of the magnetic components inside the pressure control valve. The pressure tolerance Δp, which is proportional to the magnetic flux I, is therefore subjected to a negative influence, thus reducing the control precision of an accumulator injection system comprised of separate components that are sealed in relation to one another on the high-pressure side.